The present disclosure relates generally to a low pressure mercury vapor discharge lamp and more particularly to a hot cathode fluorescent lamp including a mercury dosing apparatus and method.
Fluorescent lamps have found widespread acceptability in the market place for a number of applications and are available in a variety of shapes and forms. For example, the lamps may be linear, curvilinear, U-bent or compact in shape as will be familiar to those having ordinary skill in the art. Typically, fluorescent lamps include a light-transmissive glass discharge tube with means, such as electrodes, providing an electric discharge to the interior of the discharge tube. A phosphor layer typically applied to the inner wall surface of the discharge tube comprises the source of the light that the lamp emits. A fill gas and mercury are sealed within the discharge tube and the mercury functions to excite the phosphors' electrons resulting in the production of light by the lamp in a manner familiar to those having ordinary skill in the art.
A known mercury dosing solution for discharge lamps involves adding liquid mercury directly to the discharge tube of the lamp through an exhaust tube having a narrow diameter. Disadvantageously, this approach requires dosing the lamp with an excess of mercury since droplets of mercury can be left in the manufacturing equipment and the exhaust tube.
Other solutions for dosing a discharge lamp involve using capsules filled with liquid mercury which can prevent losses during the manufacturing process. Disadvantageously, the technique to break the capsule to make the mercury available within the lamp is difficult and requires adding machines within the manufacturing process, thereby, presenting increased cost considerations. Still other solutions involve using a metal amalgam in fluorescent lamps. However, amalgam dosing requires special dosing equipment and a means for positioning the amalgam inside the lamp. Another solution involves using solid mercury compounds on metal holders. Disadvantageously, this approach requires additional manufacturing parts, thereby increasing the cost of the lamp.
Furthermore, mercury is a hazardous material so various governmental regulations control the manner in which mercury, including mercury that is contained within articles of commerce such as fluorescent lamps is used. Used or spent lamps containing mercury are disposed of. Consequently, it can be advantageous limit the amount of mercury incorporated into articles that are eventually disposed of.
Thus, a need exists for an improved low pressure mercury vapor discharge lamp having an improved mercury dosing apparatus and method.